U.S. patent number 7,046,460 [Application Number 10/817,174] was granted by the patent office on 2006-05-16 for image-formation optical system, and imaging system.
This patent grant is currently assigned to Olympus Corporation. Invention is credited to Toshihide Nozawa.
United States Patent |
7,046,460 |
Nozawa |
May 16, 2006 |
Image-formation optical system, and imaging system
Abstract
The invention relates to an image-formation optical system that
satisfies demands toward high performance and compactness at the
same time, and an imaging system incorporating the same. The
image-formation optical system comprises, in order from its object
side, an aperture stop S, a first positive meniscus lens L1 convex
on its object side, a second positive lens L2 having an aspheric
surface and a third negative lens L3 having an aspheric surface,
and satisfies the following condition. 0.95<.SIGMA.d/f<1.25
(1) Here .SIGMA.d is the distance on an optical axis of the
image-formation optical system from the object side-surface of the
first positive meniscus lens to the image plane side-surface of the
third negative lens, and f is the focal length of the
image-formation optical system.
Inventors: |
Nozawa; Toshihide (Hachioji,
JP) |
Assignee: |
Olympus Corporation (Tokyo,
JP)
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Family
ID: |
33095270 |
Appl.
No.: |
10/817,174 |
Filed: |
April 5, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040196575 A1 |
Oct 7, 2004 |
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Foreign Application Priority Data
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Apr 4, 2003 [JP] |
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2003-101506 |
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Current U.S.
Class: |
359/791; 359/716;
359/784 |
Current CPC
Class: |
G02B
9/12 (20130101); G02B 13/0035 (20130101) |
Current International
Class: |
G02B
9/12 (20060101) |
Field of
Search: |
;359/784,791,645,661,689,716 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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55073014 |
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Jun 1980 |
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JP |
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01-144007 |
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Jun 1989 |
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JP |
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1307712 |
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Dec 1989 |
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JP |
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02-191907 |
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Jul 1990 |
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JP |
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4016811 |
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Jan 1992 |
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JP |
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04-153612 |
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May 1992 |
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JP |
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05-188284 |
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Jul 1993 |
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JP |
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09-288235 |
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Nov 1997 |
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JP |
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075006 |
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Mar 2001 |
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JP |
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2001 100090 |
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Apr 2001 |
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JP |
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2001 174701 |
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Jun 2001 |
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JP |
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2001183578 |
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Jun 2001 |
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JP |
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Primary Examiner: Sugarman; Scott J.
Assistant Examiner: Collins; Darryl J.
Attorney, Agent or Firm: Kenyon & Kenyon LLP
Claims
I claim:
1. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein an image side surface of the third
negative lens is the aspheric surface, the image side surface of
the third negative lens is in contact with an air space, and a
total of three lens elements are used.
2. The image-formation optical system according to claim 1, which
satisfies the following condition: 0.95<.SIGMA.d/f<1.25 (1)
where .SIGMA.d is a distance on an optical axis of the
image-formation optical system from an object side-surface of the
first positive meniscus lens to an image plane side-surface of the
third negative lens, and f is a focal length of the image-formation
optical system.
3. The image-formation optical system according to claim 1, wherein
said first positive meniscus lens satisfies the following
condition: 0.3<r.sub.1/f<0.6 (2) where r.sub.1 is a radius of
curvature on an optical axis of an object side-surface of the first
positive meniscus lens, and f is a focal length of the
image-formation optical system.
4. The image-formation optical system according to claim 1, which
satisfies the following conditions: 0.5<f.sub.12/|f.sub.3|<1
(3) where f.sub.12 is a composite focal length of the first
positive meniscus lens and the second positive lens, f.sub.3 is a
focal length of the third negative lens, and f is a focal length of
the image-formation optical system.
5. The image-formation optical system according to claim 1, which
satisfies the following condition: -1<EXP/f<-0.5 (5) where
EXP is a paraxial exit pupil position as determined on the basis of
an image-formation position of the image-formation optical system
relative to an object point at infinity, and f is a focal length of
the image-formation optical system.
6. The image-formation optical system according to claim 1, wherein
the second positive lens having an aspheric surface is made up of a
plastic lens.
7. The image-formation optical system according to claim 1, wherein
the third negative lens having an aspheric surface is made up of a
plastic lens.
8. The image-formation optical system according to claim 1, which
satisfies the following condition: 0.98<.SIGMA.d/f<1.20 (1-1)
where .SIGMA.d is a distance on an optical axis of the
image-formation optical system from an object side-surface of the
first positive meniscus lens to an image plane side-surface of the
third negative lens, and f is a focal length of the image-formation
optical system.
9. The image-formation optical system according to claim 1, which
satisfies the following condition: 0.32<r.sub.1/f<0.55 (2-1)
where r.sub.1 is a radius of curvature on an optical axis of an
object side-surface of the first positive meniscus lens, and f is a
focal length of the image-formation optical system.
10. The image-formation optical system according to claim 1, which
satisfies the following condition:
0.53<f.sub.12/|f.sub.3|<0.96 (3-1) where f.sub.12 is a
composite focal length of the first positive meniscus lens and the
second positive lens, and f.sub.3 is a focal length of the third
negative lens.
11. The image-formation optical system according to claim 1, which
satisfies the following condition: 0.75<|f.sub.3|/f<1.3 (4-1)
where f.sub.3 is a focal length of the third negative lens, and f
is a focal length of the image-formation optical system.
12. The image-formation optical system according to claim 1, which
satisfies the following condition: -0.8<EXP/f<-0.6 (5-1 where
EXP is a paraxial exit pupil position as determined on the basis of
an image-formation position of the image-formation optical system
relative to an object point at infinity, and f is a focal length of
the image-formation optical system.
13. The image-formation optical system according to claim 1,
wherein lenses having a refracting power are provided only by said
first positive meniscus lens, said second positive lens and said
third negative lens.
14. An imaging system, comprising an image-formation optical system
as recited in claim 1 and an electronic image pickup device located
on an image side thereof.
15. The imaging system according to claim 14, which satisfies the
following condition: 55.degree.<2.omega.<70.degree. (6) where
.omega. is a half angle of view, and 2.omega. is a total angle of
view.
16. The imaging system according to claim 14, which satisfies the
following condition: 60.degree.<2.omega.<67.degree. (6-1)
where .omega. is a half angle of view and 2.omega. is a total angle
of view.
17. The image-formation optical system according to claim 1,
wherein the third negative lens is a bi-concave lens.
18. The image-formation optical system according to claim 1,
wherein the first positive meniscus lens, the second positive lens,
and the third negative lens are single lenses respectively.
19. An imaging system comprising an image-formation optical system
comprising, in order from an object side of said image-formation
optical system, an aperture stop, a first positive meniscus lens
convex on an object side thereof, a second positive lens having an
aspheric surface and a third negative lens having an aspheric
surface, and an image pickup device located on an image side
thereof, wherein a total of three lens elements are used in said
image-formation optical system, and said aperture stop has a fixed
shape of aperture through which light rays pass, wherein an outer
peripheral surface of said aperture is inclined in such a way as to
taper down to an optical axis toward an image plane side.
20. An imaging system comprising an image-formation optical system
comprising, in order from an object side of said image-formation
optical system, an aperture stop, a first positive meniscus lens
convex on an object side thereof, a second positive lens having an
aspheric surface and a third negative lens having an aspheric
surface, and an image pickup device located on an image side
thereof, wherein a total of three lens elements are used in said
image-formation optical system, and there is provided a lens barrel
for holding said image-formation optical system and said image
pickup device, wherein said aperture stop is molded integrally of
the same resin of which said lens barrel is molded.
21. An imaging system comprising an image-formation optical system
comprising, in order from an object side of said image-formation
optical system, an aperture stop, a first positive meniscus lens
convex on an object side thereof, a second positive lens having an
aspheric surface and a third negative lens having an aspheric
surface, and an image pickup device located on an image side
thereof, wherein a total of three lens elements are used in said
image-formation optical system, a lens barrel is provided for
holding said image-formation optical system, and a peripheral
surface of at least said third negative lens is inclined in such a
way as to taper down to an optical axis toward the object side for
abutment on said lens barrel.
22. An imaging system comprising an image-formation optical system
comprising, in order from an object side of said image-formation
optical system, an aperture stop, a first positive meniscus lens
convex on an object side thereof, a second positive lens having an
aspheric surface and a third negative lens having an aspheric
surface, and an image pickup device located on an image side
thereof, wherein a total of three lens elements are used in said
image-formation optical system, a lens barrel is provided for
holding said image-formation optical system, said first positive
meniscus lens takes on a circular shape as viewed from an entrance
side of said imaging system, and said third negative lens is
configured such that, as viewed from the entrance side of said
imaging system, a length thereof in a direction corresponding to a
short-side direction of an effective image pickup area of said
image pickup device is shorter than a length thereof in a direction
corresponding to a long-side direction of the effective image
pickup device.
23. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: 0.95<.SIGMA.d/f<1.25 (1) where .SIGMA.d is a
distance on an optical axis of the image-formation optical system
from an object side-surface of the first positive meniscus lens to
an image plane side-surface of the third negative lens, and f is a
focal length of the image-formation optical system.
24. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the first positive meniscus lens satisfying the following
condition: 0.3<r.sub.1/f<0.6 (2) where r.sub.1 is a radius of
curvature on an optical axis of an object side-surface of the first
positive meniscus lens, and f is a focal length of the
image-formation optical system.
25. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
conditions: 0.5<f.sub.12/|f.sub.3|<1 (3) where f.sub.12 is a
composite focal length of the first positive meniscus lens and the
second positive lens, f.sub.3 is a focal length of the third
negative lens, and f is a focal length of the image-formation
optical system.
26. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: -1<EXP/f<-0.5 (5) where EXP is a paraxial exit
pupil position as determined on the basis of an image-formation
position of the image-formation optical system relative to an
object point at infinity, and f is a focal length of the
image-formation optical system.
27. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: 0.98<.SIGMA.d/f<1.20 (1-1) where .SIGMA.d is a
distance on an optical axis of the image-formation optical system
from an object side-surface of the first positive meniscus lens to
an image plane side-surface of the third negative lens, and f is a
focal length of the image-formation optical system.
28. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: 0.32<r.sub.1/f<0.55 (2-1) where r.sub.1 is a
radius of curvature on an optical axis of an object side-surface of
the first positive meniscus lens, and f is a focal length of the
image-formation optical system.
29. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: 0.53<f.sub.12/|f.sub.3|<0.96 (3-1) where f.sub.12
is a composite focal length of the first positive meniscus lens and
the second positive lens, and f.sub.3 is a focal length of the
third negative lens.
30. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: 0.75<|f.sub.3|/f<1.3 (4-1) where f.sub.3 is a
focal length of the third negative lens, and f is a focal length of
the image-formation optical system.
31. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: -0.8<EXP/f<-0.6 (5-1) where EXP is a paraxial exit
pupil position as determined on the basis of an image-formation
position of the image-formation optical system relative to an
object point at infinity, and f is a focal length of the
image-formation optical system.
32. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: 55.degree.<2.omega.<70.degree. (6) where .omega.
is a half angle of view, and 2.omega. is a total angle of view; and
an electronic image pickup device located on an image side of said
optical system.
33. An image-formation optical system comprising, in order from an
object side thereof, an aperture stop, a first positive meniscus
lens convex on an object side thereof, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, wherein a total of three lens elements are used,
the image-formation optical system satisfying the following
condition: 60.degree.<2.omega.<67.degree. (6-1) where .omega.
is a half angle of view, and 2.omega. is a total angle of view; and
an electronic image pickup device located on an image side of said
optical system.
Description
This application claims the benefits of Japanese Application No.
2003-101506 filed in Japan on Apr. 4, 2003, the contents of which
are incorporated herein by this reference.
BACKGROUND OF THE INVENTION
The present invention relates generally to an image-formation
optical system and an imaging system that incorporates the same.
More particularly, the invention is concerned with imaging systems
such as digital still cameras, digital video cameras harnessing
solid-state image pickup devices, e.g., CCDs or CMOSs, and
small-format cameras, surveillance cameras that are mounted on
cellar phones and personal computers.
In recent years, electronic cameras using solid-stage image pickup
devices such as CCDs or CMOSs to take subject images have come into
wide use in place of silver-halide cameras. For imaging systems
mounted on portable computers, cellular phones, etc. of those
electronic cameras, size and weight reductions are especially
demanded.
Some conventional image-formation optical systems used with such
imaging systems are made up of one or two lenses. With those
optical systems, however, any high performance is not expectable
because of their inability to correct field curvature, as already
known from discussions about aberrations. To achieve high
performance, therefore, it is required to use three or more
lenses.
A problem with CCDs is, on the other hand, that as off-axis light
beams emerging from an image-formation optical system are incident
on an image plane at too large an angle, the ability of microlenses
to concentrate light does not satisfactorily work, causing the
brightness of an image to change noticeably between its central
area and its peripheral area. For this reason, the angle of
incidence of light rays on the CCD, i.e., the exit pupil position
is an important design consideration. For an optical system
comprising a limited number of lenses, the position of an aperture
stop is of importance.
With those problems in mind, front stop triplet type
image-formation lenses have been put forward, as disclosed
typically in Patent Publications 1 12.
Patent Publication 1
JP-A 1-144007
Patent Publication 2
JP-A 2-191907
Patent Publication 3
JP-A 4-153612
Patent Publication 4
JP-A 5-188284
Patent Publication 5
JP-A 9-288235
Patent Publication 6
JP-A 2001-75006
Patent Publication 7
JP-A 55-73014
Patent Publication 8
JP-A 1-307712
Patent Publication 9
JP-A 4-16811
Patent Publication 10
JP-A 2001-100090
Patent Publication 11
JP-A 2001-174701
Patent Publication 12
JP-A 2001-183578
However, such prior arts have a lot of problems as described
below.
With the optical systems disclosed in Patent Publications 1, 2, 3,
4 and 5, correction of coma and astigmatism due to off-axis light
rays is difficult because the first positive lenses are each in a
double-convex form. In any case, the half angle of view is limited
to about 25.degree..
With the optical system of Patent Publication 6, such adverse
influences as mentioned above are lessened by configuring the first
positive lens in a meniscus shape convex on its image side.
However, the length of the optical system is still large, failing
to achieve significant size reductions.
SUMMARY OF THE INVENTION
In view of such prior art problems as stated above, the primary
object of the present invention is to provide an image-formation
optical system that makes a sensible tradeoff between enhanced
performance and size reductions, and an imaging system that
incorporates the same.
According to the present invention, the above object is
accomplished by the provision of an image-formation optical system
comprising, in order from the object side, an aperture stop, a
first positive meniscus lens convex on an object side thereof, a
second positive lens having an aspheric surface and a third
negative lens having an aspheric surface, characterized in that the
total number of lens elements is three.
Actions and advantages of the above arrangement are now
explained.
Generally, a triplet type of +-+ construction is known for an
imaging optical system comprising three lenses. To make the length
of the optical system short, however, such a telephoto type as
known from Patent Publication 7 or the like is favorable.
Arrangements comprising two lenses are known for a telephoto type
optical system made up of a few lenses, as disclosed in Patent
Publication 8, Patent Publication 9 or the like. However, these
two-lens optical systems are proposed primarily as phototaking
lenses for filmed cameras, and so cannot be applied to digital
cameras in view of optical performance.
Patent Publications 10, 11 and 12 propose a two-lens retrofocus
type optical system of -+ construction designed to be used on
digital cameras or the like. In view of optical performance,
however, this can be applied only to digital cameras of the class
that comprises 300,000 pixels at most. In addition, the retrofocus
type renders it difficult to shorten the length of the optical
system.
In accordance with the invention aiming at size reductions by the
adoption of the telephoto type, there is provided a lens
arrangement of ++- construction that ensures performance enough to
be used with 1,000,000 pixel class digital cameras.
To diminish the angle of incidence of light rays on a CCD that is
an image pickup device, the aperture stop is located nearest to the
object side of the arrangement. In the invention wherein the number
of lenses used is reduced, the aperture stop should most
effectively be positioned on the object side, although the powers
of the lenses should preferably be determined such that the exit
pupil is positioned off toward the object side.
The first positive lens is defined by a meniscus lens that has a
curved surface of strong positive power on its object side. This
enables the principal point of the first positive lens to be moved
toward the object side, and so is favorable for shortening the
length of the optical system.
The second positive lens and the third negative lens have each an
aspheric surface primarily for the purpose of making correction for
spherical aberrations at the aspheric surface of the second
positive lens and for field curvature and distortion at the
aspheric surface of the third negative lens.
Especially with the arrangement wherein the aperture stop is
located nearest to the object side or the lenses are found on only
one side of the stop, it is difficult to correct the optical system
for off-axis aberrations such as field curvature and distortion.
However, those off-axis aberrations can be well corrected if both
surfaces of the third negative lens are defined by aspheric
surfaces.
If the optical system satisfies the following condition, then its
length can be made short at a large angle of view.
0.95<.SIGMA.d/f<1.25 (1) Here .SIGMA.d is the distance on the
optical axis of the optical system from the object side-surface of
the first positive meniscus lens to the image plane side-surface of
the third negative lens, and f is the focal length of the optical
system.
As the upper limit of 1.25 to condition (1) is exceeded, the
optical system becomes long, and as the lower limit of 0.95 is not
reached, the focal length of the optical system becomes long with
the result that the angle of view becomes narrow.
More preferably, 0.98<.SIGMA.d/f<1.20 (1-1)
The optical system of the invention should also satisfy the
following condition (2) to improve on its performance and reduce
its length. 0.3<r.sub.1/f<0.6 (2) Here r.sub.1 is the radius
of curvature on the optical axis of the object side-surface of the
first positive meniscus lens, and f is the focal length of the
optical axis.
As the upper limit of 0.6 to condition (2) is exceeded, or the
radius of curvature on the optical axis of the object side-surface
of the first positive meniscus lens becomes slacker, the principal
point of the first positive meniscus lens is shifted toward the
image plane side. This means that in order to shorten the length of
the optical system, the power of each lens must be increased,
failing to achieve any sufficient performance. Falling short of the
lower limit of 0.3 may be favorable for length reductions, but
renders it difficult to make correction for spherical aberrations
occurring at the object side surface of the first positive meniscus
lens.
More preferably, 0.32<r.sub.1/f<0.55 (2-1)
This optical system is of the telephoto type due to the positive
power of each of the first positive lens and the second positive
lens and the negative power of the third negative lens. Two
conditions, given below, are to determine the positive power and
negative power of the telephoto type in such a way as to keep
length and performance in a well-balanced state.
0.5<f.sub.12/|f.sub.3|<1 (3) 0.7<|f.sub.3|/f<1.8 (4)
Here f.sub.12 is the composite focal length of the first positive
meniscus lens and the second positive lens, f.sub.3 is the focal
length of the third negative lens, and f is the focal length of the
optical system.
Any departure from the upper limit of 1 and the lower limit of 0.5
to condition (3) will cause the positive power and the negative
power, contributing to the telephoto type, to be thrown off
balance, ending up with length increases and underperformance.
Exceeding the upper limit of 1.8 to condition (4) is unfavorable
for length reductions, because the negative power contributing to
the telephoto type becomes weak. As the lower limit of 0.7 is not
reached, the negative power contributing to the telephoto type
becomes too strong. This means that the positive power, too, must
be increased accordingly, resulting in an increase in aberrations
occurring at each lens and difficulty with which performance is
ensured.
More preferably, at least one of the following conditions should be
satisfied. 0.53<f.sub.12/|f.sub.3|<0.96 (3-1)
0.75<|f.sub.3|/f<1.3 (4-1)
Incidentally, when a CCD is used as an image pickup device, there
is a so-called shading phenomenon where as an off-axis light beam
leaving an optical system is incident on an image plane at too
large an angle, central and peripheral areas of an image vary in
brightness. With the incidence of an off-axial light beam on the
image plane at a small angle, this problem is eliminated if not
completely; however, there is another problem that the optical
system becomes long. Thus, it is preferable for the image-formation
optical system to satisfy the following condition.
-1<EXP/f<-0.5 (5) Here EXP is a paraxial exit pupil position
as determined on the basis of the image-formation position of the
image-formation optical system relative to an object point at
infinity, and f is the focal length of the image-formation optical
system.
Any departure from the upper limit of -0.5 to condition (5) will
render the optical system overly long, and any deviation from the
lower limit of -1 will cause the angle of incidence of light on the
CCD to become too large, leading to a drop of the brightness of the
peripheral area of the image.
More preferably, -0.8<EXP/f<-0.6 (5-1)
Preferably for the image-formation optical system of the invention,
either one or both of the second positive lens having an aspheric
surface and the third negative lens having an aspheric surface
should be formed of a plastic lens or lenses.
Lenses having refracting power, which form part of the
image-formation optical system, should preferably consist of three
lenses, i.e., a first positive meniscus lens, a second positive
lens and a third negative lens.
The present invention also embraces an electronic imaging system
comprising any one of the image-formation optical systems as
described above and an electronic image pickup device located on
the image side thereof.
Preferably, the electronic imaging system of the invention should
satisfy the following condition.
55.degree.<2.omega.<70.degree. (6) Here .omega. is a half
angle of view, and 2.omega. is a total angle of view.
Falling short of the lower limit of 55.degree. to condition (6)
means that the image pickup angle is not very large. On the other
hand, exceeding the upper limit of 70.degree. often results in
off-axis aberrations that are hardly corrected with a limited
number of lenses.
More preferably, 60.degree.<2.omega.<67.degree. (6-1)
The present invention also provides an imaging system comprising an
image-formation optical system comprising, in order from an object
side thereof, an aperture stop, a first positive meniscus lens
convex on its object side, a second positive lens having an
aspheric surface and a third negative lens having an aspheric
surface, and an image pickup device located on an image side
thereof, characterized in that the total of three lens elements are
used in said image-formation optical system, and said aperture stop
has a fixed shape of aperture through which light rays pass,
wherein the outer peripheral surface of said aperture is inclined
in such a way as to taper down to an optical axis toward an image
plane side.
Actions and advantages of the thus constructed imaging system are
now explained. As light reflected at a peripheral surface area of
the aperture stop enters the image-formation optical system, some
phenomena such as those known as ghosts and flares are likely to
occur. Especially on the small-format image-formation optical
system of the invention comprising, in order from its object side,
the aperture stop, the first positive meniscus lens convex on the
object side, the second positive lens having an aspheric surface
and the third negative lens having an aspheric surface, light
reflected at the peripheral surface area of the aperture stop has
relatively large influences, because the image pickup plane of the
image pickup device decreases in size, too.
To eliminate or reduce such influences by taking advantage of the
arrangement wherein the aperture stop is located nearest to the
object side, the aperture stop used herein is of a fixed aperture
shape, and the peripheral surface area of the aperture stop is
inclined at an angle of inclination larger than the angle of
incidence of a farthest off-axis light beam in such a way as to
taper down to the optical axis toward the image plane side.
With this arrangement, the light beam reflected at the peripheral
surface area of the aperture is less likely to enter the image
pickup device, so that the influences of ghosts and flares can be
eliminated or reduced.
Further, the present invention provides an imaging system
comprising an image-formation optical system comprising, in order
from an object side thereof, an aperture stop, a first positive
meniscus lens convex on its object side, a second positive lens
having an aspheric surface and a third negative lens having an
aspheric surface, and an image pickup device located on an image
side thereof, characterized by further comprising a lens barrel for
holding said image-formation optical system and said image pickup
device, wherein said aperture stop is formed integrally of the same
resin of which said lens barrel is formed.
Actions and advantages of the thus constructed imaging system are
now explained. In the imaging system of the invention, the aperture
stop is located nearest to the object side of the image-formation
optical system. The nearer a lens is positioned to the image side,
the larger the effective surface of that lens becomes. Thus, if the
lens barrel for holding those lenses is made up of the same,
easy-to-mold resin, the respective lenses can then be inserted into
the barrel from its image plane side for lens alignment,
facilitating fabrication.
If, in this case, the aperture stop is integrated with the lens
barrel, it is then possible to substantially cut off fabrication
process steps. Further, if the lens barrel itself is permitted to
have an image pickup device retaining function, it is then possible
to make dust less likely to enter the barrel.
Still further, the present invention provides an imaging system
comprising an image-formation optical system comprising, in order
from an object side of said image-formation optical system, an
aperture stop, a first positive meniscus lens convex on an object
side thereof, a second positive lens having an aspheric surface and
a third negative lens having an aspheric surface, and an image
pickup device located on an image side thereof, characterized in
that a lens barrel is provided for holding said image-formation
optical system, and a peripheral surface of at least said third
negative lens is inclined in such a way as to taper down to an
optical axis toward the object side for abutment on said lens
barrel.
Actions and advantages of the thus constructed imaging system are
now explained. In the imaging system of the invention, the aperture
stop is located nearest to the object side of the image-formation
optical system. The nearer a lens is positioned to the image side,
the larger the effective surface of that lens becomes. This is
particularly true of the third negative lens. According to this
arrangement, the lens contour conforms to off-axis light beams so
that the optical system can be slimmed down while reducing shading.
By inserting the respective lenses in the lens barrel from its
image plane side, they can be so aligned that the optical system
can be easily fabricated.
It is again preferable that the peripheral surface of the first
positive meniscus lens is inclined in such a way as to taper down
to the optical axis toward the object side, while abutting on the
lens barrel.
It is noted that the "peripheral surface" used herein means an
outer peripheral surface sandwiched between the entrance surface
side edge of a lens and the exit surface side edge of the lens.
Still further, the present invention provides an imaging system
comprising an image-formation optical system comprising, in order
from an object side of said image-formation optical system, an
aperture stop, a first positive meniscus lens convex on an object
side thereof, a second positive lens having an aspheric surface and
a third negative lens having an aspheric surface, and an image
pickup device located on an image side thereof, characterized in
that a lens barrel is provided for holding said image-formation
optical system, said first positive meniscus lens takes on a
circular shape as viewed from an entrance side of said imaging
system, and said third negative lens is configured such that, as
viewed from the entrance side of said imaging system, the length
thereof in a direction corresponding to the short-side direction of
the effective image pickup area of said image pickup device is
shorter than the length thereof in a direction corresponding to the
long-side direction of the effective image pickup device.
Actions and advantages of the thus constructed imaging system are
now explained. In the imaging system of the invention, the aperture
stop is located nearest to the object side of the image-formation
optical system. The nearer a lens is positioned to the image side,
the larger the effective surface of that lens becomes, and the
closer the shape of an effective light beam becomes to that of the
effective image pickup area of the image pickup device toward the
image plane side. Thus, the above arrangement permits the lens
contour to conform to the effective light beam, so that the optical
system can be slimmed down while shading is reduced.
It is noted that the lower or upper limit of each main condition
could be defined by the lower or upper limit of the subordinate
condition.
It is also noted that the advantages of the invention are much more
enhanced by combinations of the respective conditions as described
above.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction,
combinations of elements, and arrangement of parts which will be
exemplified in the construction hereinafter set forth, and the
scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is illustrative in section of the lens arrangement in
Example 1 of the image-formation optical system of the invention
upon focused on an object point at infinity.
FIG. 2 is a sectional view, similar to FIG. 1, of the lens
arrangement in Example 2 of the image-formation optical system
according to the invention.
FIG. 3 is a sectional view, similar to FIG. 1, of the lens
arrangement in Example 3 of the image-formation optical system
according to the invention.
FIG. 4 is a sectional view, similar to FIG. 1, of the lens
arrangement in Example 4 of the image-formation optical system
according to the invention.
FIG. 5 is a sectional view, similar to FIG. 1, of the lens
arrangement in Example 5 of the image-formation optical system
according to the invention.
FIG. 6 is an aberration diagram for Example 1 upon focused on an
object point at infinity.
FIG. 7 is an aberration diagram for Example 2 upon focused on an
object point at infinity.
FIG. 8 is an aberration diagram for Example 3 upon focused on an
object point at infinity.
FIG. 9 is an aberration diagram for Example 4 upon focused on an
object point at infinity.
FIG. 10 is an aberration diagram for Example 5 upon focused on an
object point at infinity.
FIG. 11 is illustrative in section of one embodiment of the
invention wherein the image-formation optical system of Example 1
and a CCD located on its image plane are fixed to a lens barrel
obtained by integral molding of a resin material.
FIG. 12 is a schematic, exploded view of the image-formation
optical system wherein the third negative lens is in an oval
form.
FIG. 13 is illustrative of the transmittance characteristics of one
example of a near-infrared sharp cut coat.
FIG. 14 is illustrative of the transmittance characteristics of one
example of a color filter located on the exit surface side of a
low-pass filter.
FIG. 15 is illustrative of how color filter elements are arranged
for a complementary colors mosaic filter.
FIG. 16 is illustrative of one example of the wavelength
characteristics of the complementary colors mosaic filter.
FIG. 17 is illustrative of an aperture configuration in a full
aperture state.
FIG. 18 is illustrative of a two-stage aperture configuration.
FIG. 19 is illustrative in perspective of the image-formation
optical system of the invention wherein a turret is provided with a
plurality of aperture stops of fixed shape, which have different
configurations and transmittances.
FIG. 20 is a front view of another turret that may be used in place
of that of FIG. 19.
FIG. 21 is illustrative of another turret form of light quantity
control filter available herein.
FIG. 22 is illustrative of one example of a filter that reduces
variations of light quantity.
FIG. 23 is a rear and a front view of one example of a rotary focal
plane shutter.
FIGS. 24(a), 24(b), 24(c) and 24(d) are illustrative of how the
rotary shutter curtain of the shutter of FIG. 23 is rotated.
FIG. 25 is illustrative of the image pickup operation of CCD in
interlaced mode.
FIG. 26 is illustrative of the image pickup operation of CCD in
progressive mode.
FIG. 27 is a front perspective view illustrative of the outward
appearance of a digital camera incorporating the image-formation
optical system of the invention.
FIG. 28 is a rear perspective view of the digital camera of FIG.
27.
FIG. 29 is a sectional schematic of the digital camera of FIG.
27.
FIG. 30 is a front perspective view of a personal computer in use,
in which the image-formation optical system of the invention is
incorporated as an objective optical system.
FIG. 31 is a sectional view of a phototaking optical system in the
personal computer.
FIG. 32 is a side view of the state of FIG. 30.
FIGS. 33(a) and 33(b) are a front and a side view of a cellular
phone incorporating the image-formation optical system of the
invention as an objective optical system, and FIG. 33(c) is a
sectional view of a phototaking optical system for the same.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The image-formation optical system of the invention is now
explained with reference to Examples 1 to 5. FIGS. 1 5 are
illustrative in section of the lens arrangements in Examples 1 5
upon focused on an object point at infinity. In those figures, S
represents an aperture stop, L1 a first positive lens, L2 a second
positive lens, L3 a third negative lens, CG a cover glass for an
electronic image pickup device, and I an image plane. It should be
appreciated that the cover glass CG may be provided on its surface
with a frequency region-limiting multilayer coating, and is still
allowed to have a low-pass filter function.
EXAMPLE 1
Example 1 is directed to an image-formation optical system that is
made up of, in order from its object side, an aperture stop S, a
first positive meniscus lens L1 that is convex on its object side
and has an aspheric surface on its object side, a second,
double-convex positive lens L2 that has an aspheric surface on its
image plane side, a third, double-concave negative lens L3 that has
aspheric surfaces on both its sides, and a cover glass CG, as shown
in FIG. 1. The first lens L1, second lens L2 and third lens L3 are
all formed of plastics.
The specifications for the image-formation optical system according
to this example are:
focal length f=3.83 mm,
image height=2.30 mm,
F-number=2.98, and
total angle of view 2.omega.=63.0.degree..
EXAMPLE 2
Example 2 is directed to an image-formation optical system that is
made up of, in order from its object side, an aperture stop S, a
first positive meniscus lens L1 that is convex on its object side
and has an aspheric surface on its object side, a second,
double-convex positive lens L2 that has an aspheric surface on its
image plane side, a third, double-concave negative lens L3 that has
aspheric surfaces on both its sides, and a cover glass CG, as shown
in FIG. 2. The first lens L1, second lens L2 and third lens L3 are
all formed of plastics.
The specifications for the image-formation optical system according
to this example are:
focal length f=3.79 mm,
image height=2.30 mm,
F-number=2.92, and
total angle of view 2.omega.=62.4.degree..
EXAMPLE 3
Example 3 is directed to an image-formation optical system that is
made up of, in order from its object side, an aperture stop S, a
first positive meniscus lens L1 that is convex on its object side
and has an aspheric surface on its object side, a second,
double-convex positive lens L2 that has an aspheric surface on its
image plane side, a third, double-concave negative lens L3 that has
aspheric surfaces on both its sides, and a cover glass CG, as shown
in FIG. 3. The first lens L1, second lens L2 and third lens L3 are
all formed of plastics.
The specifications for the image-formation optical system according
to this example are:
focal length f=3.85 mm,
image height=2.30 mm,
F-number=2.96, and
total angle of view 2.omega.=61.7.degree..
EXAMPLE 4
Example 4 is directed to an image-formation optical system that is
made up of, in order from its object side, an aperture stop S, a
first positive meniscus lens L1 that is convex on its object side,
a second positive meniscus lens L2 that is convex on its object
side and has aspheric surfaces on both its sides, a third negative
meniscus lens L3 that is convex on its object side and has aspheric
surfaces on both its sides, and a cover glass CG, as shown in FIG.
4. The first lens L1 is formed of glass, and both the second lens
L2 and third lens L3 are formed of plastics.
The specifications for the image-formation optical system according
to this example are:
focal length f=3.83 mm,
image height=2.30 mm,
F-number=2.74, and
total angle of view 2.omega.=61.8.degree..
EXAMPLE 5
Example 5 is directed to an image-formation optical system that is
made up of, in order from its object side, an aperture stop S, a
first positive meniscus lens L1 that is convex on its object side,
a second, double-convex positive lens L2 that has an aspheric
surfaces on an image plane side, a third, double-concave negative
lens L3 that has aspheric surfaces on both its sides, and a cover
glass CG, as shown in FIG. 5. The first lens L1 is formed of glass,
and both the second lens L2 and third lens L3 are formed of
plastics.
The specifications for the image-formation optical system according
to this example are:
focal length f=3.55 mm,
image height=2.30 mm,
F-number=2.80, and
total angle of view 2.omega.=65.2.degree..
The numerical data on each example are given below. Symbols used
hereinafter but not hereinbefore have the following meanings:
r.sub.1, r.sub.2, . . . : radius of curvature of each lens surface
d.sub.1, d.sub.2, . . . : spacing between adjacent lens surfaces
n.sub.d1, n.sub.d2, . . . : d-line refractive index of each lens
v.sub.d1, v.sub.d2, . . . : Abbe number of each lens
Here let x be an optical axis on condition that the direction of
propagation of light is positive and y be a direction orthogonal to
the optical axis. Then, aspheric configuration is given by
x=(y.sup.2/r)/[1+{1-(K+1)(y/r).sup.2}.sup.1/2]+A.sub.4y.sup.4+A.sub.6y.su-
p.6+A.sub.8y.sup.8 where r is a paraxial radius of curvature, K is
a conical coefficient, and A.sub.4, A.sub.6 and A.sub.8 are the
fourth, sixth and eighth aspheric coefficients, respectively.
EXAMPLE 1
TABLE-US-00001 r.sub.1 = .infin. (Stop) d.sub.1 = 0.10 r.sub.2 =
1.365 (Aspheric) d.sub.2 = 0.63 n.sub.d1 = 1.50913 .nu..sub.d1 =
56.20 r.sub.3 = 2.622 d.sub.3 = 0.46 r.sub.4 = 2.750 d.sub.4 = 0.70
n.sub.d2 = 4.50913 .nu..sub.d2 = 56.20 r.sub.5 = -47.775 (Aspheric)
d.sub.5 = 0.60 r.sub.6 = -5.474 (Aspheric) d.sub.6 = 0.62 n.sub.d3
= 1.57268 .nu..sub.d3 = 33.51 r.sub.7 = 2.645 (Aspheric) d.sub.7 =
0.40 r.sub.8 = .infin. d.sub.8 = 0.50 n.sub.d4 = 1.51633
.nu..sub.d4 = 64.14 r.sub.9 = .infin.
Aspherical Coefficients 2 nd surface K=-0.664
A.sub.4=7.93801.times.10.sup.-3 A.sub.6=1.59402.times.10.sup.-2
A.sub.8=-2.69710.times.10.sup.-3 5 th surface K=612.567
A.sub.4=-2.69780.times.10.sup.-2 A.sub.6=-1.22057.times.10.sup.-2
A.sub.8=4.19450.times.10.sup.-2 6 th surface K=-43.850
A.sub.4=-4.22561.times.10.sup.-1 A.sub.6=-5.25463.times.10.sup.-2
A.sub.8=-7.90009.times.10.sup.-2 7 th surface K=0.000
A.sub.4=-2.59494.times.10.sup.-1 A.sub.6=5.15201.times.10.sup.-2
A.sub.8=-4.92327.times.10.sup.-3
EXAMPLE 2
TABLE-US-00002 r.sub.1 = .infin. (Stop) d.sub.1 = 0.10 r.sub.2 =
1.313 (Aspheric) d.sub.2 = 0.84 n.sub.d1 = 1.50913 .nu..sub.d1 =
56.20 r.sub.3 = 1.488 d.sub.3 = 0.14 r.sub.4 = 2.106 d.sub.4 = 0.80
n.sub.d2 = 1.50913 .nu..sub.d2 = 56.20 r.sub.5 = -5.751 (Aspheric)
d.sub.5 = 0.38 r.sub.6 = -11.293 (Aspheric) d.sub.6 = 0.93 n.sub.d3
= 1.57268 .nu..sub.d3 = 33.51 r.sub.7 = 2.159 (Aspheric) d.sub.7 =
0.50 r.sub.8 = .infin. d.sub.8 = 0.50 n.sub.d4 = 1.51633
.nu..sub.d4 = 64.14 r.sub.9 = .infin.
Aspherical Coefficients 2 nd surface K=0.000
A.sub.4=-3.44484.times.10.sup.-2 A.sub.6=-5.44446.times.10.sup.-5
A.sub.8=0 5 th surface K=4.258 A.sub.4=-1.33824.times.10.sup.-1
A.sub.6=4.38330.times.10.sup.-2 A.sub.8=0 6 th surface K=0.000
A.sub.4=-3.99293.times.10.sup.-1 A.sub.6=2.75894.times.10.sup.-2
A.sub.8=-5.61639.times.10.sup.-2 7 th surface K=-16.238
A.sub.4=-7.90754.times.10.sup.-2 A.sub.6=1.64359.times.10.sup.-2
A.sub.8=-1.28594.times.10.sup.-3
EXAMPLE 3
TABLE-US-00003 r.sub.1 = .infin. (Stop) d.sub.1 = 0.10 r.sub.2 =
1.295 (Aspheric) d.sub.2 = 0.81 n.sub.d1 = 1.50913 .nu..sub.d1 =
56.20 r.sub.3 = 1.468 d.sub.3 = 0.15 r.sub.4 = 2.126 d.sub.4 = 0.83
n.sub.d2 = 1.50913 .nu..sub.d2 = 56.20 r.sub.5 = -6.380 (Aspheric)
d.sub.5 = 0.38 r.sub.6 = -10.735 (Aspheric) d.sub.6 = 0.90 n.sub.d3
= 1.50913 .nu..sub.d3 = 56.20 r.sub.7 = 1.967 (Aspheric) d.sub.7 =
0.50 r.sub.8 = .infin. d.sub.8 = 0.50 n.sub.d4 = 1.51633
.nu..sub.d4 = 64.14 r.sub.9 = .infin.
Aspherical Coefficients 2 nd surface K=0.000
A.sub.4=-3.71837.times.10.sup.-2 A.sub.6=7.63558.times.10.sup.-3
A.sub.8=0 5 th surface K=-5.446 A.sub.4=-1.27985.times.10.sup.-1
A.sub.6=5.14883.times.10.sup.-2 A.sub.8=0 6 th surface K=0.000
A.sub.4=-4.20900.times.10.sup.-1 A.sub.6=3.44052.times.10.sup.-2
A.sub.8=-5.77484.times.10.sup.-2 7 th surface K=-13.683
A.sub.4=-8.08690.times.10.sup.-2 A.sub.6=1.71290.times.10.sup.-2
A.sub.8=-1.33388.times.10.sup.-3
EXAMPLE 4
TABLE-US-00004 r.sub.1 = .infin. (Stop) d.sub.1 = 0.10 r.sub.2 =
1.564 d.sub.2 = 0.80 n.sub.d1 = 1.56384 .nu..sub.1 = 60.67 r.sub.3
= 3.773 d.sub.3 = 0.24 r.sub.4 = 7.599 (Aspheric) d.sub.4 = 0.80
n.sub.d2 = 1.50913 .nu..sub.d2 = 56.20 r.sub.5 = 14.647 (Aspheric)
d.sub.5 = 0.52 r.sub.6 = 2.891 (Aspheric) d.sub.6 = 0.96 n.sub.d3 =
1.50913 .nu..sub.d3 = 56.20 r.sub.7 = 1.382 (Aspheric) d.sub.7 =
0.50 r.sub.8 = .infin. d.sub.8 = 0.50 n.sub.d4 = 1.51633
.nu..sub.d4 = 64.14 r.sub.9 = .infin.
Aspherical Coefficients 4 th surface K=-109.458
A.sub.4=-2.05429.times.10.sup.-2 A.sub.6=0 A.sub.8=0 5 th surface
K=-1000.000 A.sub.4=-7.44229.times.10.sup.-2
A.sub.6=7.88033.times.10.sup.-2 A.sub.8=0 6 th surface K=1.208
A.sub.4=-3.88181.times.10.sup.-1 A.sub.6=1.90917.times.10.sup.-1
A.sub.8=-7.73931.times.10.sup.-2 7 th surface K=-7.065
A.sub.4=-8.13811.times.10.sup.-2 A.sub.6=2.21922.times.10.sup.-2
A.sub.8=-3.71919.times.10.sup.-3
EXAMPLE 5
TABLE-US-00005 r.sub.1 = .infin. (Stop) d.sub.1 = 0.10 r.sub.2 =
1.781 d.sub.2 = 0.70 n.sub.d1 = 1.77250 .nu..sub.d1 = 49.60 r.sub.3
= 2.507 d.sub.3 = 0.66 r.sub.4 = 2.129 d.sub.4 = 0.60 n.sub.d2 =
1.50913 .nu..sub.d2 = 56.20 r.sub.5 = -43.514 (Aspheric) d.sub.5 =
0.51 r.sub.6 = -17.179 (Aspheric) d.sub.6 = 0.60 n.sub.d3 = 1.57268
.nu..sub.d3 = 33.51 r.sub.7 = 2.468 (Aspheric) d.sub.7 = 0.50
r.sub.8 = .infin. d.sub.8 = 0.50 n.sub.d4 = 1.51633 .nu..sub.d4 =
64.14 r.sub.9 = .infin.
Aspherical Coefficients 5 th surface K=1000.000
A.sub.4=7.54185.times.10.sup.-2 A.sub.6=-2.75072.times.10.sup.-2
A.sub.8=0 6 th surface K=-1000.000 A.sub.4=-2.70404.times.10.sup.-1
A.sub.6=8.62262.times.10.sup.-2 A.sub.8=-4.41128.times.10.sup.-2 7
th surface K=0.000 A.sub.4=-1.98374.times.10.sup.-1
A.sub.6=4.98813.times.10.sup.-2
A.sub.8=-5.21494.times.10.sup.-3
FIGS. 6 to 10 are aberration diagrams indicative of spherical
aberrations, comae, distortions and chromatic aberrations of
magnification in Examples 1 to 5 upon focused on an infinite object
point.
The image-formation optical system according to each of the above
examples is of a small size, and still creates images of good
quality.
Set out below are the values of conditions (1) to (6) in each of
the above examples.
TABLE-US-00006 Condition Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 (1) 1.02
1.08 1.06 1.13 1.15 (2) 0.36 0.35 0.34 0.41 0.50 (3) 0.93 0.90 0.89
0.56 0.76 (4) 0.79 0.81 0.83 1.73 1.05 (5) -0.64 -0.65 -0.65 -0.63
-0.72 (6) 63.0.degree. 62.4.degree. 61.7.degree. 61.8.degree.
65.2.degree.
Throughout the above examples of the invention, the aspheric
surfaces are all made up of plastics; however, it is understood
that they may be made up of glass. For instance, much higher
performance could be achieved by use of glass having a refractive
index higher than that of the plastic material used in any of the
above examples. Likewise, the use of special low-dispersion glass
could be more effective at correction of chromatic aberrations. The
use of a plastic material of low hygroscopicity is particularly
preferable because degradation of performance due to environmental
changes is substantially reduced (for instance, Zeonex made by
Nippon Zeon Co., Ltd.).
With a view to cutting off unnecessary light such as ghosts and
flares, it is acceptable to rely upon a flare stop in addition to
the aperture stop S. For instance, that flare stop may be
interposed at any desired position between the aperture stop S and
the first lens L1, the first lens L1 and the second lens L2, the
second lens L2 and the third lens L3, and the third lens L3 and the
image plane I. Alternatively, the lens barrel may be used to cut
off flare light rays or another member may be used as the flare
stop. Such flare stops may be obtained by direct printing, coating,
seal bonding on the optical system, etc., and configured in any
desired form such as circular, oval, rectangular, polygonal forms
or forms surrounded with functional curves. The flare stop used may
be designed to cut off not only harmful light beams but also light
beams such as coma flare around the screen.
Each lens may have been provided with an antireflection coating for
the purpose of reducing ghosts and flares. Multicoatings are
preferred because of having the ability to reduce ghosts and flares
effectively. Alternatively, infrared cut coatings may have been
applied on lens surfaces, cover glass surfaces or the like.
Focus adjustment may be carried out by focusing. Focusing may be
performed by moving the whole lenses or extending or retracting
some lenses.
A drop, if any, of brightness of the peripheral area of an image
may be reduced by the shifting of the CCD microlenses. For
instance, the design of CCD microlenses may be changed in
association with the angle of incidence of light rays at each image
height, or decreases in the quantity of light at the peripheral
area of the image may be corrected by image processing.
FIG. 11 is illustrative of one embodiment of the invention wherein
an image-formation optical system 5 according to Example 1 and a
CCD unit 6 located at an image plane I thereof are fixed to a lens
barrel 7 obtained by integral molding of a resin material; FIG. 11
is a sectional view of that embodiment including the optical axis
of the image-formation optical system 5, as taken along the
diagonal direction of the image plane I of the CCD unit 6. As
shown, an aperture stop S is attached to the lens barrel 7 by
integral molding, so that the lens barrel 7 for holding the
image-formation optical system 5 can be easily fabricated. Integral
incorporation of the aperture stop S in the lens barrel 7
considerably cuts back on fabrication steps, and providing the lens
barrel 7 with a function of holding the CCD unit 6 comprising a CCD
as an image pickup device prevents entrance of dust, etc. in the
lens barrel 7.
As can be seen from FIG. 11, the peripheral surface 8 of each of
the first positive lens L1 and the third negative lens L3 in the
image-formation optical system 5 is inclined in such a way as to
taper down to the optical axis toward the object side, so that the
tapering surface can be fixed to the lens barrel 7 while abutting
thereon. Thus, the lenses L1 and L2 can be fitted from the image
plane side in the lens barrel 7, so that they can be positioned in
alignment.
As shown in the schematic exploded perspective view of FIG. 12, the
first positive lens L1 and the second positive lens L2 in the
image-formation optical system retained in the lens barrel 7 molded
of plastics are each of a circular shape, and the third negative
lens L3 is of an oval shape wherein the uppermost and lowermost
portions of a circle are cut out, as viewed from the entrance side
of the imaging system. As shown, the peripheral surfaces 8 of the
first positive lens L1 and the third negative lens L3 taper down
toward the aperture stop S side. The inner surface of the lens
barrel 7 is inclined in association with those tapering surfaces,
too.
Thus, the first positive lens L1 is configured to be circular as
viewed from the entrance side of the imaging system, and the third
negative lens L3 is configured such that, as viewed from the
entrance side, its length in the direction corresponding to the
short-side direction of the effective image pickup area of the
image pickup device CCD is shorter than its length in the direction
corresponding to the long-side direction of the effective image
pickup area, so that the contours of the first positive lens L1,
the second positive lens L2 and the third negative lens L3 in the
image-formation lens system can conform to an effective light beam.
In this embodiment, too, the tapering peripheral surface 8 of each
of the first positive lens L1 and the third negative lens L3 in the
image-formation optical system 5 is fixed to the inner surface of
the lens barrel 7 while abutting thereon, so that the lenses L1 and
L3 can be fitted from the image plane side in the lens barrel 7 and
positioned in alignment.
As shown in the sectional view of FIG. 11, it is desired that the
peripheral surface of the aperture in the aperture stop S be
inclined with respect to the lens L1 side, so that the corner of
that peripheral surface having an angle of inclination larger than
that of the effective light beam and substantially nearest to the
lens side can act as a stop. Thus, a light beam reflected at the
peripheral surface of the aperture in the aperture stop S is less
likely to enter the image pickup device CCD, thereby making it
possible to lessen the influences of ghosts and flares.
In each example, the cover glass CG may be provided with a
near-infrared sharp cut coat on its entrance surface side. This
near-infrared sharp cut coat is designed to have a transmittance of
at least 80% at 600 nm wavelength and a transmittance of up to 10%
at 700 nm wavelength. More specifically, the near-infrared sharp
cut coat has a multilayer structure made up of such 27 layers as
mentioned below provided that the design wavelength is 780 nm.
TABLE-US-00007 Substrate Material Physical Thickness (nm) .lamda./4
1st layer Al.sub.2O.sub.3 58.96 0.50 2nd layer TiO.sub.2 84.19 1.00
3rd layer SiO.sub.2 134.14 1.00 4th layer TiO.sub.2 84.19 1.00 5th
layer SiO.sub.2 134.14 1.00 6th layer TiO.sub.2 84.19 1.00 7th
layer SiO.sub.2 134.14 1.00 8th layer TiO.sub.2 84.19 1.00 9th
layer SiO.sub.2 134.14 1.00 10th layer TiO.sub.2 84.19 1.00 11th
layer SiO.sub.2 134.14 1.00 12th layer TiO.sub.2 84.19 1.00 13th
layer SiO.sub.2 134.14 1.00 14th layer TiO.sub.2 84.19 1.00 15th
layer SiO.sub.2 178.41 1.33 16th layer TiO.sub.2 101.03 1.21 17th
layer SiO.sub.2 167.67 1.25 18th layer TiO.sub.2 96.82 1.15 19th
layer SiO.sub.2 147.55 1.05 20th layer TiO.sub.2 84.19 1.00 21st
layer SiO.sub.2 160.97 1.20 22nd layer TiO.sub.2 84.19 1.00 23rd
layer SiO.sub.2 154.26 1.15 24th layer TiO.sub.2 95.13 1.13 25th
layer SiO.sub.2 160.97 1.20 26th layer TiO.sub.2 99.34 1.18 27th
layer SiO.sub.2 87.19 0.65 Air
The aforesaid near-infrared sharp cut coat has such transmittance
characteristics as shown in FIG. 13.
A low-pass filter is provided on its exit surface side with a color
filter or coating for reducing the transmission of colors at such a
short wavelength range as shown in FIG. 14, thereby making the
color reproducibility of an electronic image much higher.
Preferably, that filter or coating should be designed such that the
ratio of the transmittance of 420 nm wavelength with respect to the
highest transmittance of a wavelength that is found in the range of
400 nm to 700 nm is at least 15% and that the ratio of 400 nm
wavelength with respect to the highest wavelength transmittance is
up to 6%.
It is thus possible to reduce a discernible difference between the
colors perceived by the human eyes and the colors of the image to
be picked up and reproduced. In other words, it is possible to
prevent degradation in images due to the fact that a color of short
wavelength less likely to be perceived through the human sense of
sight can be readily seen by the human eyes.
When the ratio of the 400 nm wavelength transmittance is greater
than 6%, the short wavelength region less likely to be perceived by
the human eyes would be reproduced with perceivable wavelengths.
Conversely, when the ratio of the 420 nm wavelength transmittance
is less than 15%, a wavelength range perceivable by the human eyes
is less likely to be reproduced, putting colors in an ill-balanced
state.
Such means for limiting wavelengths can be more effective for
imaging systems using a complementary colors mosaic filter.
In each of the aforesaid examples, coating is applied in such a way
that, as shown in FIG. 14, the transmittance for 400 nm wavelength
is 0%, the transmittance for 420 nm is 90%, and the transmittance
for 440 nm peaks or reaches 100%.
With the synergistic action of the aforesaid near-infrared sharp
cut coat and that coating, the transmittance for 400 nm is set at
0%, the transmittance for 420 nm at 80%, the transmittance for 600
nm at 82%, and the transmittance for 700 nm at 2% with the
transmittance for 450 nm wavelength peaking at 99%, thereby
ensuring more faithful color reproduction.
The low-pass filter is made up of three different filter elements
stacked one upon another in the optical axis direction, each filter
element having crystal axes in directions where, upon projected
onto the image plane, the azimuth angle is horizontal (=0.degree.)
and .+-.45.degree. therefrom. Three such filter elements are
mutually displaced by a .mu.m in the horizontal direction and by
SQRT(1/2).times.a in the.+-.45.degree. direction for the purpose of
moire control, wherein SQRT means a square root.
The image pickup plane I of a CCD is provided thereon with a
complementary colors mosaic filter wherein, as shown in FIG. 15,
color filter elements of four colors, cyan, magenta, yellow and
green are arranged in a mosaic fashion corresponding to image
pickup pixels. More specifically, these four different color filter
elements, used in almost equal numbers, are arranged in such a
mosaic fashion that neighboring pixels do not correspond to the
same type of color filter elements, thereby ensuring more faithful
color reproduction.
To be more specific, the complementary colors mosaic filter is
composed of at least four different color filter elements as shown
in FIG. 15, which should preferably have such characteristics as
given below.
Each green color filter element G has a spectral strength peak at a
wavelength G.sub.p,
each yellow filter element Y.sub.e has a spectral strength peak at
a wavelength Y.sub.p,
each cyan filter element C has a spectral strength peak at a
wavelength C.sub.p, and
each magenta filter element M has spectral strength peaks at
wavelengths M.sub.P1 and M.sub.P2, and these wavelengths satisfy
the following conditions. 510 nm<G.sub.P<540 nm 5
nm<Y.sub.P-G.sub.P<35 nm -100 nm<C.sub.P-G.sub.P<-5 nm
430 nm<M.sub.P1<480 nm 580 nm<M.sub.P2<640 nm
To ensure higher color reproducibility, it is preferred that the
green, yellow and cyan filter elements have a strength of at least
80% at 530 nm wavelength with respect to their respective spectral
strength peaks, and the magenta filter elements have a strength of
10% to 50% at 530 nm wavelength with their spectral strength
peak.
One example of the wavelength characteristics in the aforesaid
respective examples is shown in FIG. 16. The green filter element G
has a spectral strength peak at 525 nm. The yellow filter element
Y.sub.e has a spectral strength peak at 555 nm. The cyan filter
element C has a spectral strength peak at 510 nm. The magenta
filter element M has peaks at 445 nm and 620 nm. At 530 nm, the
respective color filter elements have, with respect to their
respective spectral strength peaks, strengths of 99% for G, 95% for
Y.sub.e, 97% for C and 38% for M.
For such a complementary colors filter, such signal processing as
mentioned below is electrically carried out by means of a
controller (not shown) (or a controller used with digital
cameras).
For luminance signals, Y=|G+M+Y.sub.e+C|.times.1/4 For chromatic
signals, R-Y=|(M+Y.sub.e)-(G+C)| B-Y=|(M+C)-(G+Y.sub.e)| Through
this signal processing, the signals from the complementary colors
filter are converted into R (red), G (green) and B (blue)
signals.
Now for, it is noted that the aforesaid near-infrared sharp cut
coat may be located anywhere on the optical path, and that the
number of low-pass filters may be either two as mentioned above or
one.
The aperture stop S is used for controlling the quantity of light
in the imaging system of the invention. For this aperture stop, for
instance, a variable stop may be used, which comprises a plurality
of stop blades with a variable aperture for controlling the
quantity of light. FIG. 17 is illustrative of one exemplary stop
configuration upon full aperture, and FIG. 18 is illustrative of
one exemplary configuration upon two-stage aperture. In FIGS. 17
and 18, OP stands for an optical axis, Da six stop blades, and Xa
and Xb apertures. In the invention, only two aperture
configurations, i.e., full-aperture configuration (FIG. 17) and a
stop value (two-stage stop, FIG. 18) providing an F-number that
satisfies given conditions may be used.
It is acceptable to use a turret provided with a plurality of
aperture stops that are of fixed shape yet having different
configurations or transmittances so that any of the aperture stops
can be located on the optical axis on the object side of the
image-formation optical system depending on the necessary
brightness, thereby slimming down the stop mechanism. It is also
acceptable to select from a plurality of aperture stops located on
the turret one where the quantity of light is minimized, and
fitting therein a light quantity decreasing filter that has a
transmittance lower than those of other aperture stops. This
prevents the aperture diameter of the stops from becoming too
small, helping reduce degradation, if any, of image-formation
performance due to diffraction occurring with a small aperture
diameter of the stops.
FIG. 19 is a perspective view illustrative of one exemplary
construction of this case. At an aperture stop S position on the
optical axis on the object side of the first positive lens L1 in
the image-formation optical system, there is located a turret 10
capable of brightness control at 0 stage, -1 stage, -2 stage, -3
stage and -4 stage.
The turret 10 is composed of an aperture 1A for 0 stage control,
which is defined by a maximum stop diameter, circular fixed space
(with a transmittance of 100% with respect to 550 nm wavelength),
an aperture 1B for -1 stage correction, which is defined by a
transparent plane-parallel plate having a fixed aperture shape with
an aperture area nearly half that of the aperture 1A (with a
transmittance of 99% with respect to 550 nm wavelength), and
circular apertures 1C, 1D and 1E for -2, -3 and -4 stage
corrections, which have the same aperture area as that of the
aperture 1B and are provided with ND filters having the respective
transmittances of 50%, 25% and 13% with respect to 550 nm
wavelength.
By turning the turret 10 around a rotating shaft 11, any one of the
apertures is located at the stop position, thereby controlling the
quantity of light.
Instead of the turret 10 shown in FIG. 19, it is acceptable to use
a turret 10' shown in the front view of FIG. 20. This turret 10'
capable of brightness control at 0 stage, -1 stage, -2 stage, -3
stage and -4 stage is located at the stop S position on the optical
axis on the object side of the first positive lens L1 in the
image-formation optical system.
The turret 10' is composed of an aperture 1A' for 0 stage control,
which is defined by a maximum stop diameter, circular fixed space,
an aperture 1B' for -1 stage correction, which is of a fixed
aperture shape with an aperture area nearly half that of the
aperture 1A', and apertures 1C', 1D' and 1E' for -2, -3 and -4
stage corrections, which are of fixed shape with decreasing areas
in this order.
By turning the turret 10' around a rotating shaft 11, any one of
the apertures is located at the stop position thereby controlling
the quantity of light.
To achieve further thickness reductions, the aperture in the
aperture stop S may be fixed in terms of shape and position, so
that the quantity of light may be electrically controlled in
response to signals from the image pickup device. Alternatively,
the quantity of light may be controlled by insertion or
de-insertion of an ND filter in or from other space in the lens
system, for instance, in or from between the third negative lens L3
and the CCD cover glass CG. One example of this is shown in FIG.
21. As shown, it is acceptable to use a turret-form filter that
comprises a turret 10'' having a plain or hollow aperture 1A'', an
aperture 1B'' defined by an ND filter having a transmittance of
1/2, an aperture 1C'' defined by an ND filter having a
transmittance of 1/4, an aperture 1D'' defined by an ND filter
having a transmittance of 1/8, etc. For light quantity control, any
of the apertures is located anywhere in the optical path by turning
the turret around a center rotary shaft.
For the light quantity control filter, it is also acceptable to use
a filter surface capable of performing light quantity control in
such a way as to reduce light quantity variations, for instance, a
filter in which, as shown in FIG. 22, the quantity of light
decreases concentrically toward its center in such a way that for a
dark subject, uniform transmittance is achieved while the quantity
of light at its center is preferentially ensured, and for a bright
subject alone, brightness variations are made up for.
Still alternatively, the aperture stop S may be defined by
blackening a part of the peripheral portion of the first positive
lens L1 on its entrance surface side.
When the imaging system of the invention is implemented in the form
of, for instance, a camera wherein images are stored as still-frame
ones, it is preferable to locate the light quantity control shutter
in an optical path.
For that shutter, for instance, use may be made of a focal plane
shutter, rotary shutter or liquid crystal shutter that is located
just before the CCD. Alternatively, the aperture shutter itself may
be constructed in a shutter form.
FIG. 23 is illustrative of one example of the shutter used herein.
FIGS. 23(a) and 23(b) are a rear and a front view of a rotary focal
plane shutter that is a sort of the focal plane shutter. Reference
numeral 15 is a shutter substrate that is to be located just before
the image plane or at any desired position in the optical path. The
substrate 15 is provided with an aperture 16 through which an
effective light beam through an optical system is transmitted.
Numeral 17 is a rotary shutter curtain, and 18 a rotary shaft of
the rotary shutter curtain 17. The rotary shaft 18 rotates with
respect to the substrate 15, and is integral with the rotary
shutter curtain 17. The rotary shaft 18 is engaged with gears 19
and 20 on the surface of the substrate 15. The gears 19 and 20 are
connected to a motor not shown.
As the motor not shown is driven, the rotary shutter curtain 17 is
rotated around the rotary shaft 18 via the gears 19 and 20.
Having a substantially semi-circular shape, the rotary shutter
curtain 17 is rotated to open or close the aperture 16 in the
substrate 15 to perform a shutter role. The shutter speed is then
controlled by varying the speed of rotation of the rotary shutter
curtain 17.
FIGS. 24(a) to 24(d) are illustrative of how the rotary shutter
curtain 17 is rotated as viewed from the image plane side. The
rotary shutter curtain 17 is displaced in time order of (a), (b),
(c), (d) and (a).
By locating the aperture stops of fixed shape and the light
quantity control filter or shutter at different positions in the
lens system, it is thus possible to obtain an imaging system in
which, while high image quality is maintained with the influence of
diffraction minimized, the quantity of light is controlled by the
filter or shutter, and the length of the lens system can be cut
down as well.
In the invention, electrical control may be performed in such a way
as to obtain still-frame images by extracting a part of electrical
signals of the CCD without recourse to any mechanical shutter. CCD
image pickup operation is now explained with reference to FIGS. 25
and 26. FIG. 25 is illustrative of CCD image pickup operation
wherein signals are sequentially read in the interlaced scanning
mode. In FIG. 25, Pa, Pb and Pc are photosensitive blocks using
photodiodes, Va, Vb and Vc are CCD vertical transfer blocks, and Ha
is a CCD horizontal transfer block. The A field is an odd-number
field and the B field is an even-number field.
In the arrangement of FIG. 25, the basic operation takes place in
the following order: (1) accumulation of signal charges by light at
the photosensitive block (photoelectric conversion), (2) shift of
signal charges from the photosensitive block to the vertical
transfer block (field shift), (3) transfer of signal charges at the
vertical transfer block (vertical transfer), (4) transfer of signal
charges from the vertical transfer block to the horizontal transfer
block (line shift), (5) transfer of signal charges at the
horizontal transfer block (horizontal transfer), and (6) detection
of signal charges at the output end of the horizontal transfer
block (detection). Such sequential reading may be carried out using
either one of the A field (odd-number field) and the B field
(even-number field).
When the interlaced scanning CCD image pickup mode of FIG. 25 is
applied to TV broadcasting or analog video formats, the timing of
accumulation at the A field and the B field lags by 1/60. When,
with this timing lag uncorrected, a frame image is constructed as a
DSC (digital spectrum compatible) image, there is blurring such as
a double image in the case of a subject in motion. In this CCD
image pickup mode, the A field and B field are simultaneously
exposed to light to mix signals at adjacent fields. After processed
by a mechanical shutter upon the completion of exposure, signals
are independently read from the A field and the B field for signal
synthesis.
In the invention, while the role of the mechanical shutter is
limited to only prevention of smearing, signals are sequentially
read out of the A field alone or signals are simultaneously read
out of both the A field and the B field in a mixed fashion, so that
a high-speed shutter can be released irregardless of the driving
speed of the mechanical shutter (because of being controlled by an
electronic shutter alone), although there is a drop of vertical
resolution. The arrangement of FIG. 25 has the merit of making size
reductions easy, because the number of CCDs in the vertical
transfer block is half the number of photodiodes forming the
photosensitive block.
FIG. 26 is illustrative of CCD image pickup operation wherein the
sequential reading of signals is performed in the progressive mode.
In FIG. 26, Pd to Pf are photosensitive blocks using photodiodes,
Vd, Ve and Vf are CCD vertical transfer blocks and Hb is a CCD
horizontal transfer block.
In FIG. 26, signals are read in order of the arranged pixels, so
that charge accumulation reading operation can be all
electronically controlled. Accordingly, exposure time can be cut
down to about ( 1/10,000 second). The arrangement of FIG. 26 has
the demerit of making it more difficult to achieve size reductions
because of an increased number of vertical CCDs as compared with
the arrangement of FIG. 25. However, the invention is applicable to
the mode of FIG. 25 as well as to the mode of FIG. 26 because of
such merits as mentioned above.
The present imaging system constructed as described above may be
applied to phototaking systems where object images formed through
image-formation optical systems are received at image pickup
devices such as CCDs, inter alia, digital cameras or video cameras
as well as PCs and telephone sets that are typical information
processors, in particular, easy-to-carry cellular phones. Given
below are some such embodiments.
FIGS. 27, 28 and 29 are conceptual illustrations of a phototaking
optical system 41 for digital cameras, in which the image-formation
optical system of the invention is incorporated. FIG. 27 is a front
perspective view of the outward appearance of a digital camera 40,
and FIG. 28 is a rear perspective view of the same. FIG. 29 is a
sectional view of the construction of the digital camera 40. In
this embodiment, the digital camera 40 comprises a phototaking
optical system 41 including a phototaking optical path 42, a finder
optical system 43 including a finder optical path 44, a shutter 45,
a flash 46, a liquid crystal monitor 47 and so on. As the shutter
45 mounted on the upper portion of the camera 40 is pressed down,
phototaking takes place through the phototaking optical system 41,
for instance, the image-formation optical system according to
Example 1. An object image formed by the phototaking optical system
41 is formed on the image pickup plane of a CCD 49 via a cover
glass CG provided with a near-infrared cut coat and having a
low-pass filter function. An object image received at CCD 49 is
shown as an electronic image on the liquid crystal monitor 47 via
processing means 51, which monitor is mounted on the back of the
camera. This processing means 51 is connected with recording means
52 in which the phototaken electronic image may be recorded. It is
here noted that the recording means 52 may be provided separately
from the processing means 51 or, alternatively, it may be
constructed in such a way that images are electronically recorded
and written therein by means of floppy discs, memory cards, MOs or
the like. This camera may also be constructed in the form of a
silver-halide camera using a silver-halide film in place of CCD
49.
Moreover, a finder objective optical system 53 is located on the
finder optical path 44. An object image formed by the finder
objective optical system 53 is in turn formed on the field frame 57
of a Porro prism 55 that is an image-erecting member. In the rear
of the Porro prism 55 there is located an eyepiece optical system
59 for guiding an erected image into the eyeball E of an observer.
It is here noted that cover members 50 are provided on the entrance
sides of the phototaking optical system 41 and finder objective
optical system 53 as well as on the exit side of the eyepiece
optical system 59.
With the thus constructed digital camera 40, it is possible to
achieve high performance and compactness, because the phototaking
optical system 41 is of high performance and compactness.
In the embodiment of FIG. 29, plane-parallel plates are used as the
cover members 50; however, it is acceptable to use powered
lenses.
FIGS. 30, 31 and 32 are illustrative of a personal computer that is
one example of the information processor in which the
image-formation optical system of the invention is built as an
objective optical system. FIG. 30 is a front perspective view of a
personal computer 300 in use, FIG. 31 is a sectional view of a
phototaking optical system 303 in the personal computer 300, and
FIG. 32 is a side view of the state of FIG. 30. As shown in FIGS.
30, 31 and 32, the personal computer 300 comprises a keyboard 301
via which an operator enters information therein from outside,
information processing or recording means (not shown), a monitor
302 on which the information is shown for the operator, and a
phototaking optical system 303 for taking an image of the operator
and surrounding images. For the monitor 302, use may be made of a
transmission type liquid crystal display device illuminated by
backlight (not shown) from the back surface, a reflection type
liquid crystal display device in which light from the front is
reflected to show images, or a CRT display device. While the
phototaking optical system 303 is shown as being built in the upper
right portion of the monitor 302, it may be located somewhere
around the monitor 302 or keyboard 301.
This phototaking optical system 303 comprises, on a phototaking
optical path 304, an objective lens 112 comprising the
image-formation optical system of the invention (roughly shown) and
an image pickup device chip 162 for receiving an image. These are
built in the personal computer 300.
Here a cover CG having a low-pass filter function is additionally
applied onto the image pickup device chip 162 to form an integral
imaging unit 160, which can be fitted into the rear end of the lens
barrel 113 of the objective lens 112 in one-touch operation. Thus,
the assembly of the objective lens 112 and image pickup device chip
162 is facilitated because of no need of alignment or control of
surface-to-surface spacing. The lens barrel 113 is provided at its
end (not shown) with a cover glass 114 for protection of the
objective lens 112.
An object image received at the image pickup device chip 162 is
entered via a terminal 166 in the processing means of the personal
computer 300, and shown as an electronic image on the monitor 302.
As an example, an image 305 taken of the operator is shown in FIG.
30. This image 305 may be shown on a personal computer on the other
end via suitable processing means and the Internet or telephone
line.
FIGS. 33(a), 33(b) and 33(c) are illustrative of a telephone set
that is one example of the information processor in which the
image-formation optical system of the invention is built in the
form of a phototaking optical system, especially a
convenient-to-carry cellular phone. FIG. 33(a) and FIG. 33(b) are a
front and a side view of a cellular phone 400, respectively, and
FIG. 33(c) is a sectional view of a phototaking optical system 405.
As shown in FIGS. 33(a), 33(b) and 33(c), the cellular phone 400
comprises a microphone 401 for entering the voice of an operator
therein as information, a speaker 402 for producing the voice of
the person on the other end, an input dial 403 via which the
operator enters information therein, a monitor 404 for displaying
an image taken of the operator or the person on the other end and
indicating information such as telephone numbers, a phototaking
optical system 405, an antenna 406 for transmitting and receiving
communication waves, and processing means (not shown) for
processing image information, communication information, input
signals, etc. Here the monitor 404 is a liquid crystal display
device. It is noted that the components are not necessarily
arranged as shown. The phototaking optical system 405 comprises, on
a phototaking optical path 407, an objective lens 112 comprising
the image-formation optical system of the invention (roughly shown)
and an image pickup device chip 162 for receiving an object image.
These are built in the cellular phone 400.
Here a cover glass CG having a low-pass filter function is
additionally applied onto the image pickup device chip 162 to form
an integral imaging unit 160, which can be fitted into the rear end
of the lens barrel 113 of the objective lens 112 in one-touch
operation. Thus, the assembly of the objective lens 112 and image
pickup device chip 162 is facilitated because of no need of
alignment or control of surface-to-surface spacing. The lens barrel
113 is provided at its end (not shown) with a cover glass 114 for
protection of the objective lens 112.
An object image received at the image pickup device chip 162 is
entered via a terminal 166 in processing means (not shown), so that
the object image can be displayed as an electronic image on the
monitor 404 and/or a monitor at the other end. The processing means
also include a signal processing function for converting
information about the object image received at the image pickup
device chip 162 into transmittable signals, thereby sending the
image to the person at the other end.
It is here understood that each of the embodiments mentioned above
could be modified in various fashions without any departure from
the scope of what is claimed.
As can be seen from the foregoing, the present invention can
provide a high-performance yet small-format image-formation optical
system, and a small-format yet high-performance imaging system
incorporating the same.
* * * * *